Fuel pump

ABSTRACT

A fuel pump including a charge pump for delivering discrete pulses of high pressure fuel sequentially to the several cylinders of an engine has an automatic system, effective at low loads, to improve combustion efficiency and decrease air pollution. A reciprocable shuttle piston is disposed between the high pressure generating chamber of the charge pump and a second chamber which is selectively connected to a supply conduit past a by-pass restriction provided by the metering valve. The metering valve passes a measured charge of fuel to the pressure chamber prior to each pumping stroke, and at low engine loads, connects the second chamber with the supply conduit during alternate pumping strokes so that the shuttle piston is free to move to increase the volume of the pressure chamber to store the charge of fuel, prevent pressure build-up and delivery of the charge to the engine. Prior to the next pumping stroke, another charge is delivered to the pressure chamber, and continued communication of the second chamber with the supply conduit moves the shuttle piston to reduce the volume of the pressure chamber an amount equal to the stored charge so that a double charge of fuel is pressurized and delivered to the engine. As engine load increases, and the metering valve opens to increase the measured charge to the pressure chamber, the by-pass restriction becomes smaller and the charges of fuel delivered during successive pumping strokes become equal when the by-pass restriction is closed. In a variant, the second chamber for the shuttle is selectively connected to a supply conduit by a passage which by-passes the metering valve so that the pump may be used for an engine having one-half the number of cylinders for which the pump is designed. A valve in the by-pass passage is closed when the pump is used for an engine having the designed number of cylinders and opened when used with an engine having one-half that number.

United States Patent Dec. 5, 1972 Baxter 1 1 FUEL PUMP [72] Inventor: Leonard N. Baxter, Windsor, Conn. [73] Assignee: Stanadyne, Inc., Windsor, Conn.

[22] Filed: Feb. 3, 1971 [21] Appl. No.: 112,370

Related US. Application Data Primary Examiner--Robert M. Walker Attorney-Prutzman, Hayes, Kalb & Chilton [57] ABSTRACT A fuel pump including a charge pump for delivering discrete pulses of high pressure fuel sequentially to the several cylinders of an engine has an automatic system, effective at low loads, to improve combustion efficiency and decrease air pollution. A reciprocable shuttle piston is disposed between the high pressure generating chamber of the charge pump and a second chamber which is selectively connected to a supply conduit past a by-pass restriction provided by the metering valve. The metering valve passes a measured charge of fuel to the pressure chamber prior to each pumping stroke, and at low engine loads, connects the second chamber with the supply conduit during alternate pumping strokes so that the shuttle piston is free to move to increase the volume of the pressure chamber to store the charge of fuel, prevent pressure build-up and delivery of the charge to the engine. Prior to the next pumping stroke, another charge is delivered to the pressure chamber, and continued communication of the second chamber with the supply conduit moves the shuttle piston to reduce the volume of the pressure chamber an amount equal to the stored charge so that a double charge of fuel is pressurized and delivered to the engine. As engine load increases, and the metering valve opens to increase the measured charge to the pressure chamber, the by-pass restriction becomes smaller and the charges of fuel delivered during successive pumping strokes become equal when the by-pass restriction is closed.

In a variant, the second chamber for the shuttle is selectively connected to a supply conduit by a passage which by-passes the metering valve so that the pump may be used for an engine having one-half the .number for an engine having the designed :number of cylinders and opened when used with an engine having one-half that number.

' 14 Claims, 7 Drawing Figures P'A'TENTEDuEc 51972 SHEEI 1 BF 2 1% w Q Q U Q;

A Nw I r QW k 5 h g I M h I. l mini x g mum Nw E H 2 a w w 3 w/ d it 1LHH, I Q. & o QR an NR 0 v, Q GE O INVENTOR. LEONARD N. BAXTER ATTORNEYS BACKGROUND ANDSUMMARYOF THE INVENTION 1 The present invention relates to fuel pumps conventionally employed for supplying measured charges of fuel to an associated internal combustion engine and more particularly to such a pump for an engine of the compression-ignition type.

At low loads, the minimum power output required from an engine for its continued operation is to over come the friction losses of the engine. Because the power output from each cylinder of a multicylinder engine needed to compensate for the friction losses is small, the'relative amount of fuel required is small and the combustion efficiency is adversely affected due to lower temperatures developed by the combustion of the fuel in the combustion chamber. As a result, the combustion of the fuel is degraded, and there is a marked increase in the exhaust of the products of combustion which most adversely affect air pollution. Where less than all of the cylinders of the. engine are tired under low load conditions, the power output per firing cylinder, and hence the combustion efficiency, increases. For example, if one-half of the cylinders are tired, the load output required per cylinder to carry the friction load is doubled with a resultant improvement in combustion efficiency and lessening in air pollution problems. It is an object of this invention to provide a unique fuel injection system foran internal combustion engine which improves combustion efficiency of an associated engine at low loads.

Another object of this invention is to provide a unique fuel injection pump for an internal combustion engine which, at low loads, adds to and subtracts from the quantity of measured charges of fuel delivered to the several cylinders of the engine during selected ones of a series of pumping strokes according to a prescribed pattern. Included in this object is the provision of a fuel metering system which increases the quantity of measured charge of alternate strokes and decreases the measured charge of fuel delivered by the pump during the remaining strokes to produce the alternate firing of the cylinders of the engine.

Another object of this invention is to provide a fuel injection pump of the type described wherein the quantity of the measured charges of the fuel delivered to the non-firing cylinder gradually increases as load is applied to the engine so that the nonfiring cylinders gradually pick up their proportionate share of the load.

Another object of this invention is to provide a fuel injection pump of the type described wherein the metering valve automatically regulates the fuel delivered on sequential strokes of the charge pump.

Another object of this invention is to provide a fuel injection pump of the type described wherein the mechanism for modifying the charges 'of fuel delivered on sequential strokes is inactive when the metering valve is opened a predetermined amount.

Still another object of the invention is to provide a pump suitable for use with two different engines having a 2:1 cylinder ratio.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a longitudinal cross-sectional view, partly broken away, of a fuelinjection pump illustrating a preferred embodiment of the present invention;

FIG. 2 is an enlarged fragmentary cross-sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary cross-sectional view taken along lines 3--3 of FIG. 2 illustrating the passages between the metering valve and the charge P p;

FIG. 4 is an enlarged fragmentary cross-sectional view taken along the line 44 of FIG. 3 illustrating the functioning of the metering valve in the present invention;

FIG. 5 is a view similar to FIG. 4 further illustrating the functioning of the metering valve;

FIG. 6 is a fragmentary cross-sectional view taken along the lines 6-6 of FIG. 3; and

FIG. 7 is a view similar to FIG. 4 illustrating a modified form of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring nowto the drawing in detail, the fuel pump 10 exemplifying the present invention is shown to be of the type adapted to supply measured pulses or charges of fuel to the several fuel injection nozzles of an internal combustion engine. Apump housing 12 having a cover. 14 secured by fasteners 16 rotatably supports a pump rotor 18 and a connected drive shaft 20 having a tapered end for receiving a driving gear, not shown, to which the shaft 20 is keyed.

A vane-type transfer or low pressure supply pump 22 driven by the rotor 18 receives fuel from a reservoir, not shown, via pump inlet 24 and delivers fuel under pressure via axial conduits 28, and annulus 31 to a metering valve 32. A transfer pump pressure regulating valve, generally denoted by the numeral 34, of the type disclosed and described in US. Pat. No. 2,833,934 entitled Pressure Responsive Valve For Fuel Pumps which issued on Apr. 28, 1959, provides for regulating the output pressure of the transfer pump and returns excess fuel to the pump inlet 24.. The regulator 34 is designed to provide transfer pump output pressure which increases with engine speed in order to meet the increased fuel requirements of the engine at higher speeds and to provide a fuel pressure usable for operating auxiliary mechanisms of the fuel pump.

A high pressure charge pump 36 driven by the rotor 18 comprises a pair of opposed plungers 38 reciprocable in a diametral bore in the rotor. The charge pump 36 receives metered fuel from the metering valve 32 through a plurality of angularly spaced radial passages 40 adapted for sequential registration with a diagonal inlet passage 42 as the rotor 18 is rotated. Fuel under high pressure is delivered by the charge pump through an axial bore 46 in the rotor to a radial distributor passage 48 adapted for sequential registration with a plurality of angularly spaced outlet passages 50 (only one of which is shown) which communicate, respectively, with the individual fuel injection nozzles of the engine through discharge fittings 51 spaced around the periphery of the housing 12. A delivery valve 52 in the axial bore 46 operates in a known manner to achieve sharp cut-off of fuel to the nozzles and eliminate fuel dribble into the engine combustion chamber. Theangularly spaced radial inlet passages 40 and the angularly spaced outlet passages 50 are located to provide registration respectively with the diagonal inlet passage 42 during the intake stroke of the plungers 38 and with the outlet passage 48 during the compression stroke of the plungers.

An annular cam 54 having a plurality of pairs of diametrically opposed camming lobes is provided for actuating the charge pump plungers 38 inwardly for pressurizing the charge of fuel therein. A pair of rollers 56 and roller shoes 58 are mounted in radial alignment with the plungers 38 by a rotor driven carrier, not shown, for camming the plungers inwardly. For timing the distribution of fuel to the fuel nozzles in correlation with engine operation, the annular cam 54 may be angularly adjustable by a suitable timing mechanism 55.

A plurality of governor weights 62, angularly spaced about the pump shaft 20, provide a variable bias on a sleeve 64 which engages governor plate 66 to urge it clockwise as viewed in FIG. 1 about a supporting pivot 68. The governor plate is urged in the opposite pivotal direction by a compression spring 70 having a bias which is adjustable by a lever 72 operated by a shaft 74 which may be suitably connected to the throttle arm 75. The governor plate is connected for controlling the angular position of the metering valve 32 by a control arm 76 fixed to the metering valve and by a link 78 pivotally connected to the control arm and normally biased by the tension spring, not shown, into engagement with the governor plate 66.

As is well-known, the quantity or measure of the charge of fuel delivered by the charge pump 36 is readily controlled by varying the restriction to the fuel passage offered by metering valve 32. In the usual manner, the pump governor controls the angular position of the metering valve to govern an associated engine at a selected speed under changing load conditions. As best shown in FIGS. 4 and 5, the rotation of the metering valve 32 under the control of the pump governor varies the restriction 108 offered by the metering valve between the passages 30 and 40 and thus varies the fuel delivered by the pump to maintain the associated engine at a speed determined by the setting of the governor.

In accordance with this invention, means are provided for adding to and subtracting from the quantity of the measured charges of fuel delivered by the pump by selected pumping strokes at low power output of the engine, and the illustrated embodiment is specifically designed for the alternate firing of the cylinders of an eight cylinder engine at low speeds.

Referring to FIGS. 2-6 of the drawing, a branch passageway 80 selectively communicates with. supply passageway 30 via restriction 106 dependent upon the angular setting of the metering valve 32.

With increasing load, the metering valve 32 (FIG. rotates counterclockwise so as to close off restriction 106 to cut off communication between passages 30 and 80 and prevent the flow of fuel therebetween. Under such circumstances, the metering valve 32 controls the delivery of fuel from passage 30, 40 to deliver uniform charges of fuel to each pumping stroke of the pump.

At low loads, however, the metering valve is rotated toward its extreme clockwise position to provide communication (FIG. 4) between passages 30 and for the operation of the pump as described below.

As shown in FIGS. 3 and 6, the passage 80 downstream of the metering valve communicates with diagonal passage 82 and annulus 84 which, in turn, communicates with a plurality (shown as being four in number) of radial passageways 86 uniformly spaced about the periphery of the rotor 18. Passageways 86, in turn, communicate with a chamber 88 through a pair of connected diagonal passageways 90 and 92 formed in the distributor rotor 18. As illustrated, the chamber 88 is sealed by a cap 94 and forms a closed cylinder for reciprocable piston 96, the movement of which is limited as by its engagement with the cap 94 in one direction and the engagement of stop ring 98 provided on the piston with the shoulder surrounding the bore 100 in which the piston is mounted for reciprocation.

The piston 96 serves to isolate the chamber 88 from the chamber 102 between the charge pump pistons 38 in which the charges of fuel are pressurized.

With the passageway 90 (FIG. 6) positioned as indicated at 90a and the cam lobes of cam 54 having a relative angular position so as to urge the pistons 38 toward each other, the passageway 90 is not in communication with any one of the passageways 86, and thus the movement of the shuttle 96 upwardly as viewed in FIG. 3 (to the right as viewed in FIG. 2) is blocked since any pressure increase in the chamber 102 produces an equal and opposite pressure in the chamber 88 on the other end of the piston. Accordingly, the fuel within the chamber 102 is pressurized and passes through delivery passage 46 to the one of the several discharge fittings 51 which is in registry with distributor passage 48 to deliver fuel to the associated engine nozzle.

As the rotor 18 continues its counterclockwise rotation (FIG. 6), the passageway 42 comes into registry with a passageway 40 so that fuel passing the metering valve 32 may enter the chamber 102 between the pistons 38 to deliver another pulse or charge of fuel thereto. Further counterclockwise rotation of rotor 18 causes the cam lobes of the cam 54 again to cause the movement of the pistons 38 toward each other to reduce the volume of the chamber 102, it being understood that passage 42 has rotated out of registry with feed passage 40 from the metering valve. With an eight cylinder engine, the cam 54 has cam lobes every 45 to produce eight pumping strokes every rotation of distributor rotor 18. However, because of the communication between passage 90, as shown at 90b in phantom, and a passage 86 (FIG. 6), any increase in the pressure in chamber 102 will urge the shuttle 96 upwardly (FIG. 3) causing reverse flow from passage 80 to passage 30 past restriction 106 since, as shown in FIG. 4, the metering valve 32 is positioned (FIG. 4) to provide communication between the chamber 88 and feed passage 30 via passages 92, 90, 86, 82 and 80 past restriction 106. While the fuel in passage 30 is pressurized to a level of, say, 50 p.s.i., the reverse flow from the chamber 88 to the passage 30 is not seriously affected since the pressure normally produced in .the

chamber 102 by the charge pump is of the order of,say, 2800 psi. or more. Thus, because of the communication between the passage 90 and a passage 86 resulting from the peripherally enlarged end 104 thereof, during this pumping stroke the pressure in delivery passage 46 does not reach the level to open the injection nozzle for the cylinder scheduled to receive the pulse or charge of fuel in chamber 102 through delivery passage 48 and a discharge fitting 51. Thus, the pulse or charge remains in chamber 102. a

After the rollers 56 have reached the top of the cam lobes of the cam 54 and begin to move apart, the end 104 of passage 86 (FIG. 6) remains in communication with the passage 90 so that the low pressure of the fuel in the feed passage 30 causes a forward flow of fuel past the restriction 106 (FIG. 4) through passages 80, 82, 86, 90, and 92'into the chamber 88 to move the shuttle 96 downwardly as viewed in FIG. 3. In addition, the passage 42 again comes into registry with a passage 40 to deliver another charge or pulse of fuel into the chamber 102 in the usual manner. As explained above,

this will occur when the rotor 18 has rotated 45 further in the counterclockwise direction and the passage 90 is positioned between a pair of passages 86 as indicated by the phantom lines 900 of FIG. 6. With the passage 90 so positioned, the shuttle 96 may not move upward (FIG. 3) since there is no registry between passage 90 and one of the passages 86. Accordingly, the double charge of fuel in the chamber 102 will be pressurized and delivered through passage 46 and a discharge fitting 51 to an associated engine nozzle. In this respect, it will be apparent that the movement of the shuttle 96 to its lower position as viewed in FIG. 3, will add the pulse or charge which was stored in chamber 102 and not pressurized during the preceding pumping stroke when the passage 90 was positioned as indicated at 90b. Thus, at no load, the fuel so. pressurized is twice the normal size of the pulse or charge delivered to the chamber 102 during a single registry of passages 40 and 42.

The further counterclockwise rotation of the rotor 18 will cause a unit charge of fuel to enter chamber 102, but due to the registry of passage 90 with passage 86-during the following pumping stroke, there will be no discharge of any fuel from chamber 102. Rather, the shuttle 96 will move upwardly (FIG. 3) as hereinbefore described to temporarily store the unit charge in chamber 102.

The next pumping stroke will again find the passage 90 out of registry with the passage 86 so that the pistons 38 will pressurize a double charge of fuel to the associated engine.

With such operation of the engine in accordance with the illustrated embodiment, it will be apparent that the same total quantity of fuel is delivered to the engine under no-load conditions but that no fuel is delivered to alternate cylinders, and a double charge of fuel is delivered to the remaining cylinders. This dou firing, the combustion temperature is higher with the result that there is better combustion and less objectionable exhaust of undesirable air pollutants and smoke.

It will be understood that as the load on the engine increases, the metering valve 32 will rotate counterclockwise (FIGS. 4 and 5) so as to gradually increase the fuel delivered past restriction 108. At the same time, the reciprocating movement of the shuttle 96 is reduced by virtue of the increased restriction offered to reverse flow of fuel from chamber 88 to said passage 30 via restriction 106. Accordingly, as the load increases, the metering valve gradually limits the movement of the shuttle 96 to provide a reduced differential of the fuel delivered to alternate cylinders of the engine during consecutive pumping strokes. Finally, when the metering valve 32 completely closes the restriction 106, the shuttle 96 maintains a fixed position during each pumping stroke so that it does not add to or subtract from the charges of fuel in chamber 102 during any pumping stroke regardless of the relative position of passage 90 to passages 86. At such time and under any heavier engine load, each cylinder receives the same quantity of fuel as the other cylinders to carry its full share of the load on the engine.

DESCRIPTION OF ANOTHER PREFERRED FORM OF THE INVENTION In the form of the invention illustrated by FIG. 7, the passage does not communicate with the passage 30 past the metering valve through restriction 106 as shown in FIG. 4. Instead, a separate passage 120 bypassing metering valve 32 provides communication between supply passage 30 and passage 80. The bypass passage 120 is provided with an on/off control valve 122. When the valve 122 is in its open position,'the operation of the pump is the same as when metering valve 32 is in the position illustrated in FIG. 4. That is to say, one pumping stroke of the charge pistons 38 moves the shuttle 96 to the right as viewed in FIG. 2 with the fuel in the shuttle chamber 88 being returned to the passage 30 through bypass passage 120. Prior to the next succeeding pumping stroke, fuel from the passage 30 flows through passages 120 and 80 and moves the shuttle 96 to the left as viewed in FIG. 2 to feed the charge stored in chamber 100 into pumping chamber 102. This, coupled with the metered charge entering the pumping chamber 102 past metering valve 32, which adds an equal amount of fuel to the pumping chamber 102, causes a double charge to be delivered by the pump on the next subsequent pumping stroke (the rotor 18 (FIG. 6) being rotated to a position where the passage is out of registry with a passage 86).

In the design illustrated by FIG. 7 there is no difference in the delivery of fuel by sequential pumping strokes as a result of changes in speed or load since the setting of metering valve 32 does not affect the functioning of shuttle 96.

When the valve 122 is closed, the shuttle 96 is rendered inactive and the modified design illustrated by FIG. 7 will deliver a uniform charge during every pumping stroke of the pistons 38.

It will thus be seen that the variant design illustrated by FIG. 7 adapts the pump for use with two different engines having cylinder ratios of 2: 1.

As will be apparent to persons skilled in the art, vari ous modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention.

lclaim:

1. In a fuel injection pump for an internal combustion engine, a charge pump having a chamber for pressurizing measured charges of fuel for delivery to the engine, metering means for controlling the quantity of said measured charges of fuel, and means for subtracting from said measured charges of fuel delivered by the pump during selected pumping strokes and for adding to said measured charges of fuel delivered by the pump during other pumping strokes without changing the setting of said metering means.

2. A device as recited in claim 1 wherein the adding and subtracting means decreases the quantity of the measured charges of fuel on alternate strokes and increases the quantity of the fuel delivered on the remaining strokes.

3. A device as recited in claim 1 wherein the adding and subtracting means comprises a shuttle piston mounted in a cylinder communicating with the pump chamber and the shuttle piston moves back and forth in the cylinder to add to and subtract from the quantity of the measured charges of fuel delivered by the charge pump.

4. A device as recited in claim 3 wherein control means are provided to control the flow of fuel into and out of the other end of the shuttle piston cylinder to modify the quantity of the measured charges of fuel delivered by the charge pump during its pumping strokes.

5'. A device as recited in claim 4 wherein the control means is said metering means and includes a metering valve upstream of the charge pump and the shuttle piston cylinder to regulate the flow of fuel to the charge pump and to the other end of the shuttle piston cylinder.

6. A device as recited in claim 5 wherein the metering valve reduces the quantity of fuel delivered to the other end of the shuttle piston cylinder as it increases the quantity of fuel delivered to the charge pump.

7. A device as recited in claim 6 wherein the control means includes valve means disposed between the metering valve and the other end of the shuttle piston cylinder to provide communication therebetween during a portion of alternate pumping strokes of the charge pump.

8. A device as recited in claim 7 wherein the valve means provides communication between the other end of the shuttle piston cylinder and the metering valve during a portion of the suction stroke of the charge pump following the alternate pumping strokes.

9. A device as recited in claim 8 wherein the metering valve gradually reduces the quantity of fuel added to and subtracted from the measured charges delivered by the charge pump during consecutive strokes thereof as the engine power increases.

10. A device as recited in claim 9 wherein the metering valve shuts off the fuel to the other end of the shuttle piston cylinder above a pre-selected engine power output.

11. A device as recited in claim 8 wherein the valve means seals the other end of the shuttle piston cylinder during the pumping stroke of the charge pump on other than said alternate strokes.

12. A fuel pump as recited in claim 1 wherein an on/off valve is provided for selectively rendering the subtractin addi means ctive andjn tive.

13. In a%t?lin ecti o n pump or a multicy fnder internal combustion engine, a metering valve, a charge pump having a chamber for receiving measured charges of fuel through said metering valve for delivery to the several cylinders of the engine, an auxiliary cylinder having one end communicating with said chamber, a shuttle piston in said cylinder, a passage selectively connecting and disconnecting the other end of said cylinder to said metering valve for the passage of fuel therebetween, said metering valve being configured to increase the rate of flow of fuel to said auxiliary cylinder as it decreases the rate of the flow of fuel to said charge pump chamber to increase the charge of fuel in said charge pump when the auxiliary cylinder receives fuel from the metering valve during the suction stroke of the charge pump, and control means in said passage between the other end of the auxiliary cylinder and the metering valve to provide for reverse flow of fuel therethrough during a portion of selected pumping strokes of the charge pump.

14. A device as recited in claim 3 wherein said control means seals the other end of the auxiliary cylinder during alternate pumping strokes of the charge pump. 

1. In a fuel injection pump for an internal combustion engine, a charge pump having a chamber for pressurizing measured charges of fuel for delivery to the engine, metering means for controlling the quantity of said measured charges of fuel, and means for subtracting from said measured charges of fuel delivered by the pump during selected pumping strokes and for adding to said measured charges of fuel delivered by the pump during other pumping strokes without changing the setting of said metering means.
 2. A device as recited in claim 1 wherein the adding and subtracting means decreases the quantity of the measured charges of fuel on alternate strokes and increases the quantity of the fuel delivered on the remaining strokes.
 3. A device as recited in claim 1 wherein the adding and subtracting means comprises a shuttle piston mounted in a cylinder communicating with the pump chamber and the shuttle piston moves back and forth in the cylinder to add to and subtract from the quantity of the measured charges of fuel delivered by the charge pump.
 4. A device as recited in claim 3 wherein control means are provided to control the flow of fuel into and out of the other end of the shuttle piston cylinder to modify the quantity of the measured charges of fuel delivered by the charge pump during its pumping strokes.
 5. A device as recited in claim 4 wherein the control means is said metering means and includes a metering valve upstream of the charge pump and the Shuttle piston cylinder to regulate the flow of fuel to the charge pump and to the other end of the shuttle piston cylinder.
 6. A device as recited in claim 5 wherein the metering valve reduces the quantity of fuel delivered to the other end of the shuttle piston cylinder as it increases the quantity of fuel delivered to the charge pump.
 7. A device as recited in claim 6 wherein the control means includes valve means disposed between the metering valve and the other end of the shuttle piston cylinder to provide communication therebetween during a portion of alternate pumping strokes of the charge pump.
 8. A device as recited in claim 7 wherein the valve means provides communication between the other end of the shuttle piston cylinder and the metering valve during a portion of the suction stroke of the charge pump following the alternate pumping strokes.
 9. A device as recited in claim 8 wherein the metering valve gradually reduces the quantity of fuel added to and subtracted from the measured charges delivered by the charge pump during consecutive strokes thereof as the engine power increases.
 10. A device as recited in claim 9 wherein the metering valve shuts off the fuel to the other end of the shuttle piston cylinder above a pre-selected engine power output.
 11. A device as recited in claim 8 wherein the valve means seals the other end of the shuttle piston cylinder during the pumping stroke of the charge pump on other than said alternate strokes.
 12. A fuel pump as recited in claim 1 wherein an on/off valve is provided for selectively rendering the subtracting and adding means active and inactive.
 13. In a fuel injection pump for a multicylinder internal combustion engine, a metering valve, a charge pump having a chamber for receiving measured charges of fuel through said metering valve for delivery to the several cylinders of the engine, an auxiliary cylinder having one end communicating with said chamber, a shuttle piston in said cylinder, a passage selectively connecting and disconnecting the other end of said cylinder to said metering valve for the passage of fuel therebetween, said metering valve being configured to increase the rate of flow of fuel to said auxiliary cylinder as it decreases the rate of the flow of fuel to said charge pump chamber to increase the charge of fuel in said charge pump when the auxiliary cylinder receives fuel from the metering valve during the suction stroke of the charge pump, and control means in said passage between the other end of the auxiliary cylinder and the metering valve to provide for reverse flow of fuel therethrough during a portion of selected pumping strokes of the charge pump.
 14. A device as recited in claim 3 wherein said control means seals the other end of the auxiliary cylinder during alternate pumping strokes of the charge pump. 